Sensory System Chapter 9

Sensory Organs Sense Organ Touch Skin (external) Taste Tongue Smell Nose Hearing/Equilibrium Ears Sight Eyes

The Sensory System The central nervous system receives information from the internal and external environment via the sensory organs. Sensory organs are able to “sense” this information because of specialized receptors. When a receptor is triggered, it causes an action potential in the sensory neuron.

Types of Sensory Receptors 1. Mechanoreceptors – stimulated by changes in pressure or movement Found in skin and muscles 2. Thermoreceptors – stimulated by changes in temperature Found in skin 3. Pain receptors – stimulated by tissue damage Found in skin and viscera

Types of Sensory Receptors (continued) 4. Chemoreceptors – stimulated by changes in chemical concentration of substances Used for taste and smell 5. Photoreceptors – stimulated by light Found only in the eye

Sense of Touch Mechanoreceptors in the skin and viscera detect varying degrees of pressure. Free nerve endings have pain receptors and thermoreceptors.

Sense of Touch – Pain Pain is caused by chemicals released by inflamed tissues. Aspirin and ibuprofen reduce pain by blocking synthesis of these chemicals Referred pain – inside the body’s organs, pain is often felt in another area. Ex: Pain from the heart is felt in the left shoulder and arm

Senses of Taste & Smell Taste and smell are “chemical senses” Taste – tastebuds containing chemoreceptors are found in the epithelium of the tongue Papillae (bumps) on the tongue contain many receptors Receptors can distinguish between sweet, sour, salty, and bitter tastes.

Senses of Taste & Smell Smell – within the nasal cavity, chemoreceptors in the olfactory bulb are stimulated by odor molecules

Senses of Taste & Smell Smells have been shown to be linked to memories because the olfactory bulb is linked to the limbic system of the brain.

Sense of Hearing Anatomy of the Ear 1. Outer Ear – includes: pinna (external ear) auditory canal

Sense of Hearing Anatomy of the Ear 2. Middle Ear- includes: Eardrum (tympanic membrane) Ossicles – 3 small bones 1) Malleus (hammer) 2) Incus (anvil) 3) Stapes (stirrup) Eustachian tube – equalization of air pressure (“pops” ear)

Sense of Hearing Anatomy of the Ear 3. Inner Ear – includes: Semicircular canals – involved with equilibrium Cochlea – snail-shaped structure involved with hearing

Sense of Hearing How we Hear 1. Sound waves travel through the auditory canal to the eardrum. 2. The sound waves cause the eardrum to vibrate. 3. The vibration causes the malleus (hammer) to hit the incus (anvil) and then the stapes (stirrup). 4. The vibration passes to the fluid in the cochlea of the inner ear. 5. Each part of the spiral cochlea is sensitive to different frequencies of sound. 6. The auditory nerve takes impulses to the brain.

Sense of Hearing Equilibrium Mechanoreceptors in the semicircular canals detect rotation and movement of the head Little hair cells send information to the brain to cause appropriate motor output so as to correct position when it is unbalanced. Vertigo (dizziness)

Sense of Sight Anatomy of the Eye Sclera – protection (white of eye) Cornea – refracts light Vitreous humor – maintains eyeball shape Retina Rods – black & white vision Cones – color vision Optic nerve – sends impulses to brain

Sense of Sight Anatomy of the Eye Lens – focuses light Cilliary body – holds lens in place, accommodation Iris – regulates light entrance (muscle) Pupil – admits light

Sense of Sight How we see 1. Light enters through the pupil. The iris can contract or dilate to allow different amounts of light into the eye.

Sense of Sight How we see 2. Light passes through the lens and vitreous humor to the back of the eye, the retina. The lens can change shape to focus light through accommodation. Object is far  the lens flattens Object is near  the lens rounds

Sense of Sight How we see The image projected from the lens on the back of the eye is upside down.

Sense of Sight How we see 3. The retina has photoreceptor cells that detect light and send impulses to the brain. Rods – black and white vision sensitive to light; night vision Cones – color vision & detail Sensitive to bright light Blue, green, and red pigment cones detect different wavelengths of light

Sense of Sight How we see 4. Impulses from the rods and cones in the retina are sent to the optic nerve This spot on the retina has not rods or cones and creates a blind spot.

Sense of Sight How we see 5. The optic nerves from each eye cross at the optic chiasm. Input from the right eye goes to the left occipital lobe Input from the left eye goes to the right occipital lobe 6. Visual integration centers in the occipital lobe process visual input.

Vision Disorders Farsightedness: trouble seeing close-up eye too short and/or lens too weak light focuses behind retina correct with “convex” lens to add power Nearsightedness: trouble seeing far away eye is too long and/or lens is too powerful light focuses in front of retina correct with “concave” lens to reduce power

Presbyopia: Oldsightedness The crystalline lens tends to harden with age The near point of distinct vision moves further and further away from the eye with age.

Astigmatism Abnormal curvature of the cornea Light from vertical and horizontal direction do not focuses in the same point Correct with “cylindrical” lens to compensate

Color Blindness Red-green color-blindness – occurs when red or green cones or pigments are missing Due to sex-linked gene (on X chromosomes) so more common in men. Non-sex-linked condition Blue-color blindness- missing blue cones or pigments Monochromats: people who are totally colorblind, more severe

Disorders of the Eye Glaucoma Cataracts Damage to the optic nerve occurs due to increased eye pressure Can lead to blindness Cataracts Clouding of the lens that affects vision Very common in older people Figure 10.27b